Process for making planographic printing forms using a light sensitive gelatin reception layer



The present invention relates to planographic printing forms. In planographic printing, which in principle is based on the different behaviour of image and non-image areas of the printing surf-ace zones with respect to water and greasy ink, it is usual to employ treating baths or Fixagen and weakly acid wetting agents which usually contain phosphoric acid. This applies more especially to printing with offset printing machines. If it is desired to avoid changing the wetting system or the wetting agent on the machine, the preparation of printing plates which have a surface consisting of a hydrophilic but water-insoluble coating material consequently presupposes that tone-free impressions can be made from such layers in the weakly acid pH range of.4 to 7.

However, only a few of the numerous organic colloids which give hydrophilic and water-insoluble printing layers satisfy these conditions. Thus, gelatine is not very suitable for this purpose, since on the one hand this shows a very small degree of swelling and thus only a small degree of water conduction during printing in the vicinity of the isoelectric point, which is just in the said pH range of 4 to 7. On the other hand, due to the hardening of such 'gelatine layers which is necessary to produce a certain mechanical strength, the gelatine is always made more or less strongly hydrophobic. Compared with other hydrophilic colloids, such for example as carboxymethyl cellulose hardened with heavy metal salts, gelatine layers nevertheless have the advantage of being resistant to alkali and consequently suitable for carrying out photographic processes which involve an alkali development. With printing foils, the ink-receiving images of which are produced photographically, a coating with IgeI-atine as hydrophilic water-conducting colloid is consequently preferrcd. Such printing plates have, for example, been proposed in German Patents Nos. 1,011,280; 1,058,844 and 1,064,343 and also in our copending United States patent application Serial No. 815,816. On printing with these printing plates, it has proved to be difiicult to obtain absolutely tone-free prints with wetting agents in the said pH range of 4 to 7, especially when the machine is further soiled by paper dust and the like.

It has now been found that with :gelatine layers which are used for planographic printing, even when hardened to an extremely high degree and when using moistening agents with pH values between 4 and 7, completely tonefree impressions are produced if the gelatine is treated with a substantially neutral-ised aqueous hydro fluosilicic acid.

The partially neutralised hydro fluosilicic acid can be added to the gelatine prior to casting or can be introduced into the gelatine layer disposed on a support by means of an aftertreatment bath.

In the latter case, this aftertreat-ment bath can be preceded or followed by a treatment of the gelatine layer with other baths, such for example as hardening baths, solutions which contain development nuclei (if desired also silver halide solvents) for the production of silver images by the silver salt diffusion process, and others.

The degree of neutralisation of the hydro tluosilicic acid is of decisive importance as regards being able to carry out the process. A satisfactory hydrophilic effect Patented May 14, 1963 Since the neutralisation of the fluosilicic 'acid to the said pH range of 5.0 to 6.5 requires the consumption of more base than corresponds to the formula HgSiF Me2SiF +H2O it must be assumed that simultaneously with or following the neutralisation of the dibasic fluosilicic acid, there takes place a hydrolysis of the [SiF anion to perhaps silicic acid sols of unknown constitution perhaps still containing fluoride ions. The silicic acid sols occurring just in this pH range separate out as finely dispersed insoluble silicic acid particles on being introduced into or applied to the 'gelatine layers, to which particles can be ascribed the observed water-absorbing effect. However, these theoretical considerations do not in any way represent a limitation of the invention as claimed.

Basic compounds, the cations of which form watersoluble silicates, such for example as the hydroxides and carbonates of lithium, sodium and ammonium, are suitable for the neutralisation of the fluosilicic acid.

The hydro fiuosil-icic acid neutral-ised to pH of 5.0 to 6.5 is used as a 0.5 to 10 percent, preferably 1 to 5 percent, aqueous solution.

Depending on the concentration of the fluosilicic acid used and also on the nature of the cation, deposits can form with the partial neutralisation to the said pH range of 5 to 6.5, and these deposits are filtered off before using the solution.

Example 1 A paper sheet having wet-strength properties and weighing about g. per square metre is coated in a first working step with :a gelatine solution having the following composition:

parts of aqueous gelatine solution (30 percent) 170 parts of a 7 percent hydro fiuosilicic acid neutralised with soda to a pH of 5.5 to 5.8 and filtered 30 parts or" aqueous sodium thiosulphate solution (50 percent) 10 parts of aqueous saponin solution (7.5 percent) The pH value of the complete solution is 5 .5.

This solution is diluted to such a degree with a 3.5 percent hydro fluosilicic tacid also neutralised with soda to a pH of 5.5 to 5.8 and filtered, so that the gelatine coating is 2 to 4 gjm. under the given casting conditions. The cast layer is dried at 70 to 80 C.

In a second working step, the gelatine layer is then treated with the following aqueous solution:

350 parts of water 50 parts of an aqueous 1 percent solution of colloidal silver sulphide 2 parts of aqueous sodium thiosulphate solution (50 percent) 12 parts of aqueous caustic soda solution (10 percent) 6 parts of aqueous formalin solution (about 30 percent) 10 parts of aqueous saponin solution (7.5 percent) images can then be further transformed into an image receiving a greasy ink, for example in accordance with German Patents No. 1,011,280; 1,058,844 and 1,064,343.

On printing the paper foils in a reproduction machine operating by the offset process, no scumming is observed with such foils when using moistening agents in the pH range of from 4 to 7 and even very greasy printing inks, regardless of whether these are foils with silver images or converted images accepting greasy ink or foils on which the printing image is produced by non-photographic methods such as by typewriting. On the other hand, similar paper foils, in which fluosilicic acid neutralised to pH 5.5 to 5.8 had not been employed in the first casting, present more or less scumming depending on the pH value and the amount of moistening agent and the nature of the printing ink employed.

Example 2 A paper support as described in Example 1 is cast in a first working step with a gelatine solution having the following composition:

170 parts of aqueous gelatine solution (15 percent) 15 parts of aqueous sodium thiosulphate solution (50 percent) parts of aqueous saponin solution (7.5 percent) This solution is diluted with water to produce a gelatine coating of 2 to 4 g./m. and the cast layer is dried at 120 C.

In a second step, the gelatine layer has cast thereon an aqueous solution with the following composition:

370 parts of water 12 parts of aqueous caustic soda solution percent) 2 parts of aqueous formalin solution (about 30 percent) 10 parts of aqueous saponin solution (7.5 percent) The cast layer is dried at 120 C.

In a third working step, the layer has cast thereon the following aqueous solution:

III

170 parts of a 1.5 percent hydro fluosilicic acid neutralised with soda to a pH value of 5.5. to 5.8 and filtered 5 parts of saponin solution (7.5 percent) The cast layer is dried at 120 C.

In a fourth working step, the layer finally has coated thereon the following aqueous solution:

280 parts of water 20 parts of an aqueous 1 percent solution of colloidal silver sulphide 60 parts of aqueous sodium thiosulphate solution (50 percent) 10 parts of aqueous saponin solution (7.5 percent) The cast layer is dried at 120 C.

The paper coated in this way is stored for 8 days for completely hardening the gelatine layer.

If such paper foils are compared with those which lack the third casting with the partially neutralised fiuosilicic acid, only the former show no trace of toning, regardless of the printing ink used, when printing with acid moistening agents (pH 4 to 7). As already indicated under 1, this relates to both foils with silver images applied by the silver salt diffusion process and their converted images accepting greasy ink, and also to foils on which the printing image is not produced by photographic means.

Example 3 A paper support as described under 1 is coated in one working step with a gelatine solution having the following composition:

170 parts of aqueous gelatine solution (15 percent) 25 parts of aqueous 1 percent solution of colloidal silver sulphide parts of aqueous sodium thiosulphate solution (50 percent) 5 parts of aqueous saponin (7.5 percent) The solution is diluted with water until a gelatine coating of 2 to 4 g./m. is obtained under the given casting conditions and the cast layer is dried at 120 C.

In a second working step, the following aqueous solution is cast on top of the gelatine layer:

II 370 parts of water 12 parts of aqueous caustic soda solution (10 percent) 3 parts of aqueous formalin solution (about 30 percent) 10 parts of aqueous saponin solution (7.5 percent) The cast layer is dried at 120 C.

In a third working step, the layer has applied thereto the following aqueous solution:

III 170 parts of 1.5 percent hydro fluosilicic acid neutralised with soda to a pH value of 5.5 to 5.8 and filtered 5 parts of aqueous saponin solution (7.5 percent) The cast layer is dried at 120 C. and the paper coated this way is stored for 8 days.

By comparison of foils of the paper coated in this way with those which lack the third casting, it is found under the experimental conditions indicated in Example 1 that only the foil treated with partially neutralised hydro fiuosilicic acid does not show any toning.

Example 4 A paper support as described in Example 1 is coated in a first working step with the following gelatine solution:

170 parts of aqueous gelatine solution (15 percent) 5 parts of aqueous saponin solution (7.5 percent) The solution is diluted with water until a layer coating of about 4 to 6 g/rn. is obtained and the layer is dried at to C.

In a second working step, the following aqueous solutron is cast above the gelatine layer:

II 370 parts of water 12 parts of aqueous caustic soda solution (10 percent) 6 parts of aqueous formalin solution (about 30 percent) 10 parts of aqueous saponin solution (7.5 percent) The cast layer is dried at 70 to 80 C.

In a third working step, the layer has the following aqueous solution cast thereon:

III

370 parts of a 1 percent hydro fluosilicic acid neutralised with ammonium carbonate to pH 5.5 to 5.8

10 parts of aqueous saponin solution (7.5 percent) The cast layer is dried at 70 to 80 C.

In a fourth working step, the layer has the following aqueous solution cast thereon:

Here also, tone-free impressions can be produced from the foils of the paper coated in this Way, using the test conditions of Example 1, this being in contrast to a sample H1 which the third casting (ill) has been omitted.

Example 5 A paper support as described in Example 1 is treated in four Working steps as in Example 4, except that ammonium carbon-ate is replaced by lithium carbonate for the partial neutralisation of the fluosilicic acid in the third working step (III). The results are analogous to those set out in Example 4.

When the neutralised hydro fluosilicic acid is incorporated into the gelatine coating solution the amount thereof may be varied in wide limits. Preferably this amount is so chosen that to 50 g. of neutralised hydro fluosilicic acid are present per 100 g. of gelatine. Instead of sodiumthiosulphate there may also be added other silver halide solvents to the gelatine solution, such as other alkali metal thiosulphates, ammonium thiosulphate, alkaline earth thiosulphates or mixtures thereof, as for instance lithium-, calcium-, barium-, The amount of these thiosulphates may vary within about 1 to 50 g. per 100 g. of gelatine. As development nuclei there can be incorporated into the gelatine layer besides silver sulfide all other nuclei which are used in transfer layers for the silver salt diffusion process, including colloidal noble metals, such as colloidal silver or colloidal gold, and heavy metal sulfides such as zinc sulfide, cadmium sulfide or lead sulfide, these development nuclei being preferably applied in amounts of about 0.2 to 2 g. per 100 g. of gelatine.

What is claimed is:

1. In a process for producing planographic printing layers from a photographic silver halide emulsion layer by developing the exposed emulsion in contact with a light insensitive gelatin reception layer containing a binding agent, dissolving silver halide from the unexposed parts of said emulsion layer, transferring the unexposed dissolved silver halide to said reception layer, and reducing the transferred silver halide to silver, separating said emulmagnesium thiosulphate.

sion layer from said reception layer and hardening said reception layer for planographic printing, the improvement consisting of contacting the gelatin of said reception layer with an aqueous hydrofiuosilicic acid solution having a pH value of 5 to 6.5.

2. A process as claimed in claim 1 wherein the gelatin of said reception layer is a cast layer and said aqueous hydrofluosilicic acid solution is added to the gelatin prior to casting.

3. A process as claimed in claim 1 wherein said aqueous hydroiluosilicic acid solution is applied to the gelatin layer after the layer is formed.

4. A process according to claim 1 wherein said hydrofiuosilicic acid solution has a concentration of from 0,5 10 percent of hydrofluosilicic acid.

5. A process according to claim 1 wherein the pH value of said hydroiiuosilicic acid solution is adjusted by the addition of a compound selected from the class consisting of sodium hydroxide, sodiumcarbcnate, lithium hydroxide, lithium carbonate, ammonium hydroxide and ammonium carbonate.

6. A process according to claim 1 wherein the pH value of said hydrofiuosilicic acid solution is between 5.5 and 5.8.

Reterences Qited in the file of this patent UNITED STATES PATENTS 597,366 Strecker Ian. 11, 1898 1,852,447 Chapman et a1. Apr. 5, 1932 2,097,416 Neiley Oct. 26, 1937 2,161,731 Van Harpen June 6, 1939 2,184,288 Dangelmajer Dec. 26, 1939 2,261,439 Kelly Nov. 4, 1941 2,794,388 Lake at al. June 4, 1957 OTHER REFERENCES Noble: Latex in Industry, Rubber Age, N.Y., Second Ed, 1953, pages 289-291 and 355-357.

Tory: Photolithography, pub, by Graphic Arts Monthly, Chicago, 111., 1953, pages 177 and 178. 

1. IN A PROCESS FOR PRODUCING PLANOGRAPHIC PRINTING LAYERS FROM A PHOTOGRAPHIC SILVER HALIDE EMULSION LAYER BY DEVELOPING THE EXPOSED EMULSION IN CONTACT WITH A LIGHT INSENSITIVE GELATIN RECEPTION LAYER CONTAINING A BINDING AGENT, DISSOLVING SILVER HALIDE FROM THE UNEXPOSED PARTS OF SAID EMULSION LAYER, TRANSFERRING THE UNEXPOSED DISSOLVED SILVER HALIDE TO SAID RECEPTION LAYER, AND REDUCING THE TRANSFERRED SILVER HALIDE TO SILVER, SEPARATING SAID EMULSION LAYER FROM SAID RECEPTION LAYER AND HARDENING SAID RECEPTION LAYER FOR PLANOGRAPHIC PRINTING, THE IMPROVEMENT CONSISTING OF CONTACTING THE GELATIN OF SAID RECEPTION LAYER WITH AN AQUEOUS HYDROFLUOSILICIC ACID SOLUTION HAVING A PH VALVE OF 5 TO 6.5 